In the medical field, doctors display medical images obtained by imaging patients on monitors, interpret the displayed medical images, and observe the states of lesions and their changes over time. Medical image data of this type are generated by, for example,                CR (Computed Radiography) apparatus,        CT (Computed Tomography) apparatus,        MRI (Magnetic Resonance Imaging) apparatus,        PET (Positron Emission Tomography) apparatus,        SPECT image (Single Photon Emission Computed Tomography), and        ultrasound apparatus (US: Ultrasound System).        
With the aim of reducing the load of such interpretation on a doctor, an apparatus has been developed that detects, for example, an abnormal tumor shadow indicating a cancer or the like or a high-density minute calcification shadow from a medical image, and infers and presents the state of the shadow by computer processing, thereby supporting diagnosis. Such a support can reduce the load of interpretation on a doctor and improve the accuracy of an interpretation result. Such an apparatus is called a computer-aided diagnosis (CAD) apparatus.
In general, the following is a proper procedure when using such a CAD in an actual clinical case. First of all, the doctor interprets medical images first, and then refers to the diagnosis support information output from the CAD to compare it with the interpretation result obtained by himself/herself. In this operation, more specifically, the doctor associates finding information on an interpretation report, which the doctor has written by himself/herself, with finding information of the diagnosis support information calculated by the CAD to find an oversight, a detection error, a difference in finding, and the like. If, however, the CAD presents no grounds on which to infer the diagnosis support information, the doctor cannot determine whether the inference result obtained by the CAD is reliable or not. When the interpretation result obtained by the doctor differs from the result obtained by the CAD, in particular, it is important to determine the reliability of the inference result.
It is therefore necessary to provide a mechanism for presenting grounds on which the CAD system infers diagnosis support information. With regard to this, patent reference 1 discloses a technique of superimposing and displaying a marker indicating an abnormal shadow candidate and information supporting the determination of abnormality on a medical image. In addition, patent reference 2 discloses a technique of displaying features and criteria used for computer-aided detection as coded descriptors on an image. According to patent references 1 and 2 described above, it is possible to more accurately decide the types of abnormal shadow candidates by presenting the user the grounds of inference with respect to detected abnormal shadows.